Frequency modulation of klystrons



March 15, 1949. N, c, BARFORD 2,464,549

FREQUENCY MODULATION OF KLYSTRONS Filed may s, 1944 soll/rca 0f' Moor A Y lamr/N6 :mL-m65 Pim-ad Mn. is, 194s 2,464,549 FREQUENCY MODULATION F KLYSTBONS Norman Charles Barford, Hayes, England, as-

slgnor to Electric & Musical Industries Limited, Hayes, England, a company o! Great Britain Application May 3, 1944, Serial No. 533.854 In Great Britain May 5, 1943 This invention relates to the frequency modulation of oscillations generated by velocity-modulation discharge devices. In the specification of British Patent No. 548,095, dated September 24,

1942, it ls suggested in a device, employing a resonator for imparting velocity modulation to a stream of electrons and a further resonator for abstracting the high frequency energy therefrom and for feeding it back to the first resonator, to effect frequency modulation of the generated oscillations by the provision of a variable impedance coupled to the output resonator, the impedance being varied at a modulation frequency. It is apparent that in this prior proposal frequency modulation is effected by effectively varying the tuning of the output resonator. This however results in a reduction of the amplitude of the signal output and furthermore the frequency modulation is thus accompanied by unwanted amplitude modulation. The object of the present invention is to provide an improved apparatus with a view to avoiding these disadvantages.

Although the specification aforesaid refers to oscillators having two resonators which are intercoupled for the purpose of generating oscillations, osculators of the velocity-modulation type are also known which employ only a single resonator, the electron beam being velocity-modulated on passing through the. resonator and then being reected back through the resonator after the beam has become charge density modulated. The present invention can be applied both to this type of oscillator and the type of oscillator employing two resonators.

According to one feature of the present invention apparatus is provided for effecting frequency modulation comprising a velocity modulation discharge device having a pair of resonators coupled together for the generation of oscillations and means for varying the tuning of both of the resonators simultaneously at the modulation frequency so as to effect frequency modulation of the generated oscillations;

According to another feature of the invention there is provided apparatus for effecting frequency modulation comprising a velocity-modulation discharge device employing a single resonator and means for reflecting the electron stream back into the resonator for the purpose of generating oscillations and means for varying the tuning of said resonator at the modulation frequency so as to effect frequency modulation of the generated oscillations. Any suitable means may be employed for varying the tuning of said resonators. l

In order that the said invention may be clearly understood and readily carried into effect, it will now be more fully described with reference to the accompanying drawings, in which- Figure 1 is a diagrammatic view of apparatus according to the first-mentioned feature of the invention;

Fig. la is a similar view showing a detail of Fig. 1;

Figure 2 is a similar view according to the second-mentioned feature of the invention, and

Figure 3 illustrates a modification of Figure l.

Referring now to Figure 1 of the drawings, the reference numeral 3 indicates the envelope of a discharge device of the velocity-modulation type, the device comprising a pair o hollow resonators 4 and 5 through which an electron beam emanating from a cathode 6 is caused to pass. The cathode 6 is associated with a cathode shield 1 and after the electrons have passed through the resonators 4 and 5 the beam is collected by an electrode 8. The two resonators 4 and 5 are coupled together so as to function as a regenerative oscillator by means of coupling loops 9 and I0. If desired, however, the resonators 4 and 5 may be coupled together in any other suitable manner. In operation of the device the cathode 6 is maintained at a negative potential, for example, by connecting it to a tapping point on a resistance I I connected across a source of potential I2, whilst the cathode shield may be maintained at a more vnegative potential, as shown. The resonators 4 and 5 are maintained at a positive potential with respect to the cathode, whilst the electrode 8 is maintained at the same potential as that of the resonators 4 and 5 or at a slightly negative potential with respect thereto. The electron beam emanating from the cathode 6 in passing through the resonator 4 becomes velocity-modulated and in the drift space between the resonators 4 and 5 the beam becomes charge-density-modulated and the energy of the beam is then imparted to the resonator 5 as the beam passes therethrough to be collected by the electrode 8. Due to the coupling between the resonators the device functions to generate self-maintained oscillations at the frequency to which the resonators 4 and 5 are tuned. In order to effect frequency modulation of the generated oscillations the tunir`7 cf both of the resonators 4 and 5 is varied in any suitable manner. In the example shown in Figure 1, the means for varying the tuning of both resonators is shown diagrammatically as comprising variable impedances I3 and I4 which are coupled vto the resonators 4 and 5 via coupling loops I5 and i6.

A source of modulating voltage I1 is applied to the impedances I3 and I4 so that the magnitude of the impedances will be varied at the modulation frequency whereby the tuning of both resonators 4 and 5 is varied at said modulation frequency. Since the tuning of both the resonators 4 and 5 is varied at the modulation frequency the amplitude of the frequency-modulated oscillations is maintained substantially constant thus avoiding the disadvantages hereinbefore referred to. The frequency-modulated oscillations may befed-to a suitable load from a coupling loop I8, coupled to the resonator 5. Each of the variable impedances I3 and I4 may, for example, comprise a pair of plates forming a `capacity and one of the plates of each of said capacities may be varied at Ithe modulation frequency by connecting said plates to a moving coil arranged in the gap of a permanent magnet; the voltages from the source I1 being fed to the moving coils. The arrangement may then be as illustrated in Figure la. One

variable impedance includes plates X and Y ofwhich plate Y is movable. The other variable impedance includes plates X' and Y of which Y' is movable. Windings W and W in the gaps of permanent magnets Z and Z are energized by voltages from the source I'I.

It is found that the oscillator shown in Figure 1 operates most satisfactorily when the resonators 4 and 5 are tuned to resonate with an optimum diierence in their resonant frequencies. This optimum diiTerence in resonant frequencies should of course 'be maintained for the range over which `frequency-modulation is desired.

Figure 2 of the drawings illustrates apparatus according to the second-mentioned feature of the inventionin which the device 3 employs only a single resonator 4 and the electron :beam emanating from the cathode 6 is caused lto be reflected back through the resonator 4 to generate self-maintained oscillations Iby causing the electrode 8 to function as a reector by maintaining this electrode at a negative potential with respect to the resonator 4. The tuning of the resonator`4 is varied in any suitable manner to effect frequency modulation of the generated oscillations.

Instead of employing coupling loops I and I6 for eiecting frequencymodulation a waveguide may be employed having a variable quality which functions to cause variation of the tuning of the resonators 4 and 5 at the modulation frequency. Figure 3 of the drawings illustrates a portion of an electron discharge device in which the tuning of the resonators 4 and 5 is eected by the provision of waveguides. The resonators 4 and 5 are 'each provided with slot-like apertures I8 and I9 communicating with waveguides 20 and 2| of rectangular form in cross-section the minor dimension of each of which isshown in Figure 3. Ea-ch waveguide 20 and 2| may be provided with an adjustable element, included in rectangles I4' and I3 in the form of a piston or a conducting pillar projecting into said waveguides or a mass of dielectric material, the position of said adjustable element being varied in accordance with voltages from the source I1. The two resonators 4 and 5 instead of being coupled together =by loops 9 and I0 as in Figure 1 may be coupled by a waveguide indicated at 22.

W-hat I claim is:

l. Apparatus for eiecting frequency modulation comprising a velocity-modulation discharge device having a pair of resonators coupled together for the generation of oscillations, a source of modulating potentials and means coupled with said source and with saidresonators and actuated by voltages from said source for varying the tuning of both of the resonators simultaneously at the modulation -frequency so as to effect frequency modulation of the generated oscillations.

2. In an ultra high frequency signalling system, a velocity modulated discharge system including a pair of resonators and electron stream producing electrodes adjacent thereto for passing an electron stream therethrough, feed back couplings between said resonators for the gen.

eration of oscillations of ultra high frequency, a variable impedance coupled to each of said resonators, a source of modulating voltage and apparatus coupled to said source and to said variable impedances and adapted to be actuated by modulating voltage 'from said source for varying said impedances simultaneously in accordance with variations lin the magnitude of the modu lating voltage.

3. A signalling system as recited in claim 2 wherein said feed back couplings between said resonators for the generation of oscillations include a loop infeach resonator and a coupling between sa-id loops.

4. A system as recited in claim 2 wherein said variable impedan-ces each comprise a loop in the resonator and wherein-said loops are each coupled with a variable reactance and wherein said reactances are varied simultaneously in accordance with variations in the magnitude of the modulating voltage.

NORM'AN CHARLES BARFORD.

REFERENCES CITED The following references are of record in the ille of this patent:-

UNITED STATES PATENTS OTHER REFERENCES Electronics Buyers Guide, June 15, 1946. (Copy' -in Scientific Library, U. S. Patent Oilice.)

Disclaimer 2,464,549.-N0rman Uhales Bm'fom, Hayes, England. FREQUENCY MODULA- TION 0F KLYSTRONS. Patent dated Mawr. 15, 1949. Disclaimer filed Apr. 17, 1951, by the assignee, Electra@ c@ Musical Industries Limited. Hereby enters this disclaimer to claims 1 to 4, inclusive, of said patent.

[Oyfczal Gazette June 5,1951.] 

